/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory.config;

import java.io.IOException;
import java.util.Properties;

import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.core.io.support.PropertiesLoaderSupport;
import org.springframework.lang.Nullable;

/**
 * Allows for making a properties file from a classpath location available
 * as Properties instance in a bean factory. Can be used to populate
 * any bean property of type Properties via a bean reference.
 *
 * <p>Supports loading from a properties file and/or setting local properties
 * on this FactoryBean. The created Properties instance will be merged from
 * loaded and local values. If neither a location nor local properties are set,
 * an exception will be thrown on initialization.
 *
 * <p>Can create a singleton or a new object on each request.
 * Default is a singleton.
 *
 * @author Juergen Hoeller
 * @see #setLocation
 * @see #setProperties
 * @see #setLocalOverride
 * @see java.util.Properties
 */
public class PropertiesFactoryBean extends PropertiesLoaderSupport
        implements FactoryBean<Properties>, InitializingBean {

    private boolean singleton = true;

    @Nullable
    private Properties singletonInstance;


    /**
     * Set whether a shared 'singleton' Properties instance should be
     * created, or rather a new Properties instance on each request.
     * <p>Default is "true" (a shared singleton).
     */
    public final void setSingleton(boolean singleton) {
        this.singleton = singleton;
    }

    @Override
    public final boolean isSingleton() {
        return this.singleton;
    }


    @Override
    public final void afterPropertiesSet() throws IOException {
        if (this.singleton) {
            this.singletonInstance = createProperties();
        }
    }

    @Override
    @Nullable
    public final Properties getObject() throws IOException {
        if (this.singleton) {
            return this.singletonInstance;
        } else {
            return createProperties();
        }
    }

    @Override
    public Class<Properties> getObjectType() {
        return Properties.class;
    }


    /**
     * Template method that subclasses may override to construct the object
     * returned by this factory. The default implementation returns the
     * plain merged Properties instance.
     * <p>Invoked on initialization of this FactoryBean in case of a
     * shared singleton; else, on each {@link #getObject()} call.
     *
     * @return the object returned by this factory
     * @throws IOException if an exception occurred during properties loading
     * @see #mergeProperties()
     */
    protected Properties createProperties() throws IOException {
        return mergeProperties();
    }

}
